--- title: "8085 ALP: copy data within a range" subject: "Microprocessor" chapter: 2 key: "semester_4/microprocessor:alp-8085-copy-range" source: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8085-copy-range site: BCT Engineering --- # 8085 ALP: copy data within a range Microprocessor · Chapter 2: Programming with 8085 Microprocessor - Asked in: 2068 Magh, 8 marks - Video: [8085 program to transfer a block of data|Transferring a block of Data in 8085|Copy a block of data](https://www.youtube.com/watch?v=csDsuQm0Ijg) — Scratch Learners - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8085-copy-range - Whole chapter: https://www.bctengineer.com/md/semester_4/microprocessor/chapter-2 ## Question Ten no. of 8-bit data is started in memory at A000H. Write a program for 8085 microprocessor to copy the data to next table at A030H if the data is less than 70H and greater than 24H. ## Short answer Compare each byte: CPI 70H, skip if no carry (≥70H) using JNC; CPI 25H, skip if carry (<25H) using JC. Only bytes from 25H to 6FH are stored at A030H, advancing the destination pointer only when a byte is copied. ## Answer Data is copied only if 24H < data < 70H, i.e. 25H ≤ data ≤ 6FH. Two compares are used: - `CPI 70H` : no carry means data ≥ 70H, so skip. - `CPI 25H` : carry means data < 25H (data ≤ 24H), so skip. The destination pointer advances only when a byte is copied, so the selected bytes are stored consecutively from A030H. ```asm LXI H,0A000H ; HL = source table LXI D,0A030H ; DE = destination table MVI C,0AH ; ten data bytes NEXT: MOV A,M ; A = data CPI 70H ; A - 70H JNC SKIP ; A >= 70H -> not in range CPI 25H ; A - 25H JC SKIP ; A < 25H (i.e. <= 24H) -> not in range STAX D ; 25H <= A <= 6FH : copy INX D ; advance destination only on copy SKIP: INX H ; next source byte DCR C JNZ NEXT HLT ``` **Example:** data 10H, 30H, 24H, 25H, 70H, 6FH, 90H ... → copied bytes are 30H, 25H, 6FH (24H and 70H are excluded since the limits are strict). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which data values are copied when the data must be less than 70H and greater than 24H? A. 24H to 70H, both included B. 25H to 6FH, both included C. 24H to 6FH D. 25H to 70H Answer: B. Both limits are strict, so 24H and 70H are excluded. The copied range is 25H <= data <= 6FH. (Key point: Strict limits: copy only 25H to 6FH) 2. After CPI 70H, why does the program use JNC SKIP? A. No carry means A < 70H, which is out of range B. No carry means A = 70H only C. CPI 70H changes A, and JNC checks the new value D. No carry means A >= 70H, which is out of range Answer: D. CPI works out A - 70H. A borrow (CY = 1) happens only when A < 70H, so no carry means A >= 70H, which is outside the range. (Key point: CPI 70H with JNC skips data >= 70H) 3. Why is the lower check written as CPI 25H followed by JC SKIP? A. CY = 1 means A < 25H (A <= 24H), so 24H and below are skipped B. To include 24H in the copied data, as the question requires C. Because JC jumps when A is greater than the operand D. Because CPI can only compare with odd immediate values Answer: A. CPI 25H sets CY when A < 25H. Skipping on carry rejects every value up to 24H, so only values above 24H are copied. (Key point: CPI 25H with JC skips data <= 24H) 4. Why is INX D placed before SKIP and not after it? A. So DE always stays exactly 30H ahead of HL B. Because STAX D needs DE to be incremented first C. So DE moves only when a byte is copied, keeping the copies consecutive D. To count how many bytes were skipped Answer: C. Skipped bytes jump straight to SKIP, past INX D, so the destination pointer moves only after STAX D. The copied bytes therefore fill A030H onwards with no gaps. 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